With the revolution of digitizing communications ever closer to the antenna, software-defined radios (SDRs) with programmable modulation schemes and transmission rates have become a practical wireless communication platform. The concept is to exploit the radio transmission environment and choose the best modulation scheme to maximize the channel capacity and minimize the interferences in real time. The general principles of SDRs and modulation classifications or schemes are presented in the following publications which are incorporated herein in their entirety: Y. Huang and A. Polydoros, Likelihood methods for MPSK modulation classification. IEEE Trans. Commun., vol. 43, 1493-1504; J. Sills, Maximum-likelihood modulation classification for PSK/QAM. Proc. MILCOM'99, 1999, 57-61; K. Umebayshi et al., “Blind estimation of the modulation scheme adapted to noise power based on a concept of software define radio,” in Proc. in European Wireless 2002(EW2002), pp. 829-834 (2002-02); O. Menguc and F. Jondral, “Air interface recognition for a software radio system exploiting cyclostationarity,” in Proc. of the 15th IEEE Personal, Indoor and Mobile Radio Communications, Vol. 3, September 2004, pp. 1947-1951. When the signal data transmitted frame by frame, the modulation scheme in each data frame was chosen depending upon the channel SNR. The adaptive modulation scheme maintains the bit error rate (BER) below a certain threshold to ensure the quality of service (QoS) in data transmission. In pilot symbol based adaptive demodulation, a known pilot symbol is used in the transmitted data frame to indicate the modulation scheme for proper demodulation at the receiver. The disadvantage is that the pilot symbol occupies the bandwidth. In order to eliminate the pilot symbol and use the bandwidth efficiently, some research works have been conducted to migrate the military modulation classification techniques to commercial applications in selecting the modulation schemes automatically and blindly without the redundant pilot symbols.
The transmitted radio frequency (RF) signal should be demodulated at the receiver in real-time to ensure the continuous communication. However, the prior art automatic modulation classification methods are developed for signal surveillance purposes which does not intend to demodulate the signal on the fly. Those methods are extremely time consuming and complicated so that a large delay is introduced in computation and data processing. This delay may cause data collisions in the real-time transmission and degrade the QoS.
This invention proposes a rapid processing and classification method to solve the time-consuming and computationally intensive problems.